Insecta, Heteroptera, Belostomatidae

12 Pages·2017·2 MB·English

JournalofPaleontology,page1of12
Copyright©2017,ThePaleontologicalSociety
0022-3360/15/0088-0906
doi:10.1017/jpa.2017.48
The oldest predaceous water bugs (Insecta, Heteroptera, Belostomatidae),
with implications for paleolimnology of the Triassic Cow Branch Formation
Julia Criscione1 and David Grimaldi2
1DepartmentofEarthandPlanetarySciences,RutgersUniversity,610TaylorRoad,Piscataway,NJ,08854,USA〈[email protected]〉
2DivisionofInvertebrateZoology,AmericanMuseumofNaturalHistory,CentralParkWestat79thSt,NewYork,NY,10024,USA
〈[email protected]〉
Abstract.—A new genus and species of predaceous waterbugs, Triassonepa solensis n. gen. n. sp., isdescribed from
the Triassic Cow Branch Formation of Virginia and North Carolina (USA) based on ~36 adult specimens and
51 nymphs. This species is the oldest known member of the extantfamilyBelostomatidae. It is placed in a new genus
based onthe uniquestructure ofthe raptorial foreleg,inwhich the tarsusiselongateand opposed to the tibia + femur.
The fossil record of this family is reviewed and the paleoenvironmental implications of the species assemblage
preservedintheCowBranchFormationarediscussed.
Introduction Though belostomatids are widespread in Cenozoic sedi-
ments, many are still undescribed, including a Paleocene
The Heteroptera, or sucking bugs, have a long fossil record, specimenfromAlberta,Canada(MitchellandWighton,1979),
potentially spanning back to the Permian. The first putative twounnamedearlyEocenespecimensfromDenmark(Larsson,
heteropteran from this period is Paraknightia magnifica Evans, 1975;RustandAnsorge,1996),andalateOligocenespecimen
1943 from New South Wales (Evans, 1950). However, the first fromGermany(Wedmann,2000).TheextantgenusLethocerus
definitive heteropteran, Arlecoris louisi Shcherbakov, 2010, was Mayr,1853becamefairlydiverseduringtheMiocene,withtwo
recentlydescribedfromtheearliestMiddleTriassic(earlyAnisian) species (L. sulcifemoralis Říha and Kukalová, 1967, and
ofthenorthernVosgesMountainsofFrance.Thisspeciesisalso L.turgaicusPopov,1971)foundintheOligocene–Mioceneof
the earliest member of the infraorder Nepomorpha Popov, 1968, the Czech Republic and the Miocene of Russia, respectively.
a group containing the majority of truly aquatic heteropterans Additionally, two modern species, Lethocerus americanus
(BelostomatidaeLeach,1815;NepidaeLatreille,1802;Naucoridae Leidy, 1847 and Belostoma bakeri Montandon, 1913, are
Leach, 1815; Corixidae Leach, 1815; and Notonectidae Leach, reported to occur in Late Pleistocene asphalt deposits of
1815).TheNepomorphahavethebestfossilrecordofallHetero- California (Miller, 1983). See Table 1 for a complete list of
ptera(GrimaldiandEngel,2005),nodoubtbecauseoftheiraquatic fossilbelostomatidspecies.
habits,butthefossilrecordofbelostomatidsisnotyetwellstudied. Today, belostomatids have a worldwide distribution,
Modern Belostomatidae are medium- (9mm) to very large-sized althoughthemajority ofspecies arefound inthetropics. They
(110mm adult body length) swimming bugs that are efficient are represented by three subfamilies consisting of nine genera
predators, grabbing prey with raptorial forelegs, injecting potent and ~146 species (Schuh and Slater, 1995). The subfamily
salivarysecretions,andsiphoningouttheliquefiedinternaltissues Belostomatinae Lauck and Menke, 1961, is by far the largest
oftheirpreywithasharpbeak. group within Belostomatidae and contains six genera: Abedus
The earliest described belostomatid fossils are from the Stål, 1862; Appasus Amyot and Serville, 1843 (Polhemus,
Jurassic,whenthefamilyfirstdiversified.Theoldestoftheseis 1995); Belostoma Latreille, 1807; Diplonychus Laporte, 1833;
Odrowazicoris polonicus Popov, 1996, an isolated wing in Hydrocyrius Spinola, 1850; and Limnogeton Mayr, 1853. The
Hettangian-age beds of the Holy Cross Mountains of Poland. subfamily Horvathiniinae Lauck and Menke, 1961, is mono-
A number of other Jurassic species have been described generic, consisting of nine species in the genus Horvathinia
from Europe and the United States, including: Tarsabedus Montadon, 1911. The third subfamily, Lethocerinae Lauck
menkei Popov, Dolling, and Whalley, 1994; Aenictobelostoma and Menke, 1961, consists of three genera: Lethocerus Mayr,
primitivumPolhemus,2000;StygeonepafoersteriPopov,1971; 1853; Benacus Stål, 1861 (Goodwyn, 2006); and Kirkaldyia
and Nettelstedtia breitkreutzi Popov, Rust, and Brauckmann, Montandon,1909(Goodwyn,2006).
2000. The Early Cretaceous also harbored diverse species and Thecurrentbelostomatidphylogenyisbasedonmorphology
genera, including three taxa from theCratoFormation Platten- and reproductive behaviors: (Lethocerinae, (Horvathiniinae
kalk of Brazil, and a species possessing unique paddle-shaped (Belostomatinae))) (Lauck and Menke, 1961; Mahner, 1993;
metathoracic legs, Iberonepa romerali Martínez-Delclòs, Nel, Smith, 1997). Lethocerinae is the most basal taxon because it
andPopov,1995,fromLasHoyas,Spain. retainsmany charactersofNepidae (‘waterscorpions’),thesister
1
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2 JournalofPaleontology
Table1. Listoffossilbelostomatidspecies.
Species Age Formation Locality Author(s);Reference
Odrowazicorispolonicus EarlyJurassic Zagaje Poland Popov,1996
Tarsabedusmenkei EarlyJurassic “LowerLias” Dorset,England Popov,Dolling,andWhalley,1994
Lethonectesnaucoroides EarlyJurassic “LowerLias” Dorset,England Popov,Dolling,andWhalley,1994
Aenictobelostomaprimitivum MiddleJurassic Todilto NewMexico,USA Polhemus,2000
Mesobelostomumdeperditum LateJurassic Solnhofen Germany Germar,1839;Lakshminarayana,1984
Mesonepaprimordialis LateJurassic Solnhofen Germany Germar,1839;Lakshminarayana,1984
Stygeonepafoersteri LateJurassic Solnhofen Germany Popov,1971
Nettelstedtiabreitkreutzi LateJurassic Bed103 SchwarzeQuarry, Popov,Rust,andBrauckmann,2000
Nettelstedt,Germany
Araripebelostomummartinsnetoi EarlyCretaceous Crato Brazil NelandPaicheler,1992
Neponymphesgodoii EarlyCretaceous Crato Brazil Zamboni,2001
Lethocerusvetus EarlyCretaceous Crato Brazil NelandWaller,2006
Lethopterusmultinervosus EarlyCretaceous Dzun-Bain Mongolia Popov,1989
Sinobelostomaliui EarlyCretaceous Huachi-Huanhe GansuProvince,China ChouandHong,1989
Iberoneparomerali EarlyCretaceous LaHuérguina LasHoyas,Spain Martínez-Delclòs,Nel,andPopov,1995
UnnamedSpecimen Paleocene Paskapoo Alberta,Canada MitchellandWighton,1979
UnnamedSpecimen earlyEocene Fur Denmark Larsson,1975
UnnamedSpecimen earlyEocene Fur Denmark RustandAnsorge,1996
Lethocerussulcifemoralis Oligocene BechlejovicerDiatomite CzechRepublic ŘíhaandKukalová,1967
UnnamedSpecimen lateOligocene Enspel Germany Wedmann,2000
Propoissoniabeskonakensis Oligocene–Miocene — Turkey NelandPaicheler,1992
Lethocerusturgaicus Miocene Abrosimovka W.Siberia,Russia Popov,1971
Manocerusstagnans middleMiocene Shanwang ShandongProvince,China Zhang,1989
Diplonychusmicrocephalum= middleMiocene Shanwang ShandongProvince,China ZhangandZhang,1994
Sphaerodemamicrocephalum
Lethocerusamericanus LatePleistocene RanchoLaBreaAsphalt California,USA Leidy,1847;Miller,1983
Belostomabakeri LatePleistocene McKittrickAsphalt California,USA Montandon,1913;Miller,1983
group to Belostomatidae. In addition, all species of Lethocerinae the insects in this formation (Olsen et al., 1978; Fraser et al.,
are emergent-brooders, meaning that their eggs are deposited on 1996). The Cow Branch Formation is significant because it
emergentvegetationandattendedtobythemales.Incontrast,the preserves the oldest fauna of freshwater insects, which are
more derived members of Belostomatinae are back-brooders, preservedasthin,two-dimensional,silveryfilmsinamatrixof
in which eggs are deposited on the backs of their male mates. very fine-grained, black shale. Preservation is often excellent,
Horvathiniinae is placed between Lethocerinae and Belostomati- with many specimens fully articulated and microscopic details
naebecauseofitsmoreintermediatemorphologicalcharacteristics. visible.Inadditionto11ordersofinsects(FraserandGrimaldi,
Brooding behavior has not been observed in this group and its 2003; Grimaldi et al., 2005), the Solite Quarry has produced
phylogeneticpositionislesscertain(LauckandMenke,1961). numerous amphibious reptiles (Tanytrachelos ahynis Olsen,
The relationships within subfamily Belostomatinae are 1979),aglidingreptile(MecistotrachelosapeorosFraseretal.,
mostlyresolvedbasedonmorphology,withtheexceptionofthe 2007), fishfossils,dinosaurfootprints, and many plant species
genus Limnogeton. Its position has been questioned due to its (Olsenetal.,1978).
lackofraptorialforelegsandnatatorialmidandhindlegs.Lauck
and Menke (1961) noted the possibility that these characters Methods.—Specimens were viewed using a Nikon SMZ1500
may indicate a more basal position within Belostomatidae. microscope, fitted with a fiber optic ring light. This non-direc-
However, it has been placed within subfamily Belostomatinae tional, diffuse light source was necessary to illuminate the
because it exhibits back-brooding behavior (Voelker, 1968). silvery, carbonized film by which the insects are preserved.
Thispositionwassupportedinarecentphylogeneticanalysisof Inorder toexamine theminutedetails,specimens werewetted
Nepomorpha(Brożek,2014). with70%ethanoltoincreasecontrastbetweenthefossilandthe
This paper describes the earliest known species of family blackshalematrix.Photographsweretakenusingtwoseparate
Belostomatidae, Triassonepa solensis n. gen. n. sp., from the setups.SpecimensviewedattheAmericanMuseumofNatural
Late Triassic Cow Branch Formation of southern Virginia and History (AMNH) were photographed with a Nikon 16MP
northernNorthCarolina.Basedonboththespeciesassemblage cameraandNikonElementsNISsoftwareonaNikonSMZ1500
within the formation and the known habitats of modern belos- stereomicroscope.SpecimenshousedattheVirginiaMuseumof
tomatids, probable chemical and environmental conditions of NaturalHistory(VMNH)werephotographedwithaCanon6D
thedepositarediscussed. DSLR camera using Canon Utility 2 software. All specimen
measurementsweretakenusingImageJsoftware.Totallengths
ofadultsweremeasuredfromtheanteriormarginofheadtothe
Materialsandmethods
distalmarginofthe7thabdominalsegment,inordertoexclude
Locality and material.—The fossils described in this study are the8thabdominalsegment,whichprotrudestovaryingdegrees
from the Cow Branch Formation of southern Virginia and indifferentspecimens.
northernNorthCarolina,aLateTriassic(Carnian/earlyNorian,
230–220 Ma) deposit outcropping in the former Solite Quarry Repositories and institutional abbreviations.—Most of the
where>30VanHoutencyclesarepreserved.Threecycleshave material examined in this study is housed at the Virginia
yieldedinsectfossils,butonecyclehasproducedthemajorityof Museum of Natural History (VMNH), Martinsville, Virginia,
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Criscione andGrimaldi—EarliestBelostomatidfossilsfromTriassicNorthCarolina 3
USA;somespecimensaredepositedintheAmerican Museum
ofNaturalHistory(AMNH),NewYork,USA.
Systematicpaleontology
SuborderHeteropteraLatreille,1810
InfraorderNepomorphaPopov,1968
SuperfamilyNepoideaLatreille,1802
FamilyBelostomatidaeLeach,1815
GenusTriassonepanewgenus
Type species.—Triassonepa solensis n. gen. n. sp. by present
designation.
Diagnosis.—Asfortypespecies,bymonotypy.
Etymology.—The genus name is a combination of the prefix
Triasso-, for the Triassic Period from which the genus is
derived, and -nepa, a standard suffix used for the superfamily
Nepoidea.
Occurrence.—Former Solite Quarry C, Eden, Rockingham
County, North Carolina, USA (36°32'29.6556''N, 79°40'
12.8424''W); Carnian/Norian, Late Triassic, Cow Branch
Formation.
Remarks.—Triassonepa n. gen. differs from all other known
extinctandextantgeneraofBelostomatidaebythestructureof
the foreleg, in which the tarsus is elongate and opposed to the
tibia+ femur. Figure1. Triassonepa solensisn. gen.n.sp., habitus of holotype, VMNH
94671.Scalebaris2mm.
Triassonepasolensisnewgenusnewspecies
Figures1–5 Thorax.—Pronotumsmall,2.5–3.5mmwide,0.8–1.1mm
long,withconcaveanteriorandposteriormargins.Mesonotum
Holotype.—VMNH94671,male,Fig.1.
width ~1.6x pronotum width; possible pigmentation preserved
onpronotumandmesonotum.Scutellumaboutaswideaspro-
Diagnosis.—Body elongate. Head small, largely hidden notum,butwithindistinctmargins.Hemelytrawithfinecrenu-
beneath pronotum dorsally, with triangular clypeus. Pronotum lations on proximal two-thirds, reticulations on distal third;
small with concave anterior and posterior margins. Hemelytra clavusandclavalsuturedistinct;venationasshowninFigure3
withprominentclavalsuture;densereticulationsonapicalthird. (alsoFig.4.4).Hindwing,ifpresent,notpreserved.Prothoracic
Prothoraciclegsraptorial,withelongatetarsusopposedtotibia. legsraptorial(Fig.4.1);femurwideatbase(~1mm),narrowed
Metathoracic tibia and tarsus with dense setal fringe on inner distally, partially obscured by body; tarsus elongate and
(mesal) margin. Abdomen with seven visible segments (seg- opposed to tibia, tibia and tarsus of similar width, tibia length
ments2–8)andfivevisiblepairsofspiracles. ~1.1xlengthoftarsus;tarsalclawnotvisible.Mesothoraciclegs
slender, with no setae or fringe apparent; tibia ~1.3x length of
Occurrence.—Former Solite Quarry C, Eden, Rockingham entiretarsus.Metathoraciclegsslender,withdensesetalfringe
County, North Carolina, USA (36°32'29.6556''N, 79°40' oninner(mesal)marginoftibiaandtarsus(Fig.4.6);fewspe-
12.8424''W); Carnian/Norian, Late Triassic, Cow Branch cimenswithdoublesetalfringeontarsus(Fig.4.8,4.9);femur
Formation. partially obscured by body; tibia length ~1.2x tarsus length;
tarsuswithtwosegments.
Description of Adults.—The description is based on the ~36 Abdomen.—Broad, often obscured by hemelytra; length
adultspecimenscollectedtodate(Fig.2).Bodyelongate;total (7.4–8.6mm) and width (5.4–6.3mm) vary, likely due to
length (anterior margin of head, excluding clypeus, to apex of diagenetic alteration; abdominal segments 2–8 visible; dorsum
7thabdominalsegment)10.6–14.1mm(mean12.1mm). with five pairs of spiracles visible on segments 3–7. Spiracle
Head.—Small,largelyhiddenbeneathpronotumdorsally, diameter ranges from 0.26 to 0.40mm (mean 0.34mm).
with triangular clypeus. Eyes, antennae, and mouthparts not Terminalia variable, but with lateral paddle-like lobes; pair of
visible.Ocelli,ifpresent,notvisible. short processes between the lobes that resemble respiratory
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4 JournalofPaleontology
Figure2. PhotographsofadultspecimensofTriassonepasolensisn.gen.n.sp.:(1)VMNH49641;(2)VMNH53881;(3)VMNH53880;(4)VMNH94672.
Scalebarsare2mm.
tubes; two specimens (VMNH 94671, Fig. 4.12, holotype; Remarks.—Specimen VMNH 94671 was chosen as the holo-
VMNH94672,Fig.2.4)withmoreelongateterminaliaandtwo type because of the excellent preservation of its legs (Fig. 1).
distalarticulatedappendages,possiblyclaspers. Itistheonlyspecimenyetfoundwithapreservedforeleg,and
one of only two specimens with a preserved mesothoracic leg.
Though this specimen has a narrower abdomen and lacks the
Descriptionofnymphs.—Thedescriptionisbasedon51nymph stoutnessoftheotherspecimens,thisdifferenceinoverallshape
specimens.Bodyoval,narrowedatanteriorandposteriorends. can likely be attributed to diagenesis due to its morphologic
Headsmall,oftennotpreserved,nofeaturesdiscernable.Thorax similarity tothe other specimens. Additionally, it is thelargest
roughly trapezoidal with dividing line between lateral halves; specimen(14.10mm),butitisofasimilarsizetothatoftheonly
wing pads not visible. Prothoracic and mesothoracic legs not othermalespecimen(VMNH94672,Fig.2.4,13.49mm).This
preserved. Few specimens with metathoracic tarsus preserved; may indicate that males of this species were larger than the
setal fringe present, as in adults; two specimens (e.g., VMNH females,whichisunusualintheHeteroptera.
54155,Fig.5.4)withdoublesetalfringe;claws,ifpresent,not Triassonepa solensis n. gen n. sp. is the earliest known
visible. Abdomen roughly triangular; six segments visible member of the family Belostomatidae. Unfortunately, all adult
(segments3–8). specimens are preserved in dorsal aspect, concealing many
morphologicalcharacters.Thisisinterestingbecausepreserva-
tionoftheventralsurfaceisquitecommoninotherbelostomatid
Etymology.—The specific epithet is named after the former fossils (e.g., Sinobelostoma liui, Chou and Hong, 1989;
VirginiaSoliteCorporationquarries,fromwhichthespecimens Lethocerusvetus,NelandWaller, 2006).Triassonepasolensis
wererecovered. n.gen.n.sp.rangesinlengthfrom~10.6–14.1mm,placingiton
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Criscione andGrimaldi—EarliestBelostomatidfossilsfromTriassicNorthCarolina 5
Figure3. ReconstructionofTriassonepasolensisn.gen.n.sp.showingmajormorphologicalcharacters.
thesmallsideoftherangeofmodernbelostomatids(9–110mm; belostomatids have a thin tibia + tarsus opposed to the femur
SchuhandSlater,1995). (Fig. 4.2, 4.3). This raptorial foreleg appears to be less
The head of Triassonepa solensis n. gen. n. sp. is poorly specialized than those of modern belostomatids. Another
preserved in almost all specimens, preventing a detailed difference between T. solensis and modern belostomatids is
description at this time. The only feature often visible is the thepossessionofsetaeonthelegs.Modernbelostomatidshave
triangular clypeus. Neither compound eyes nor ocelli are setae on both the mesothoracic and metathoracic legs, but it
preserved,althoughtheabsenceofocellimaybeexpectedsince appearsthatthemesothoraciclegsofT.solensislackthesesetae.
modernbelostomatidsdonotpossessthem(LauckandMenke, This might suggest that instead of using these legs for
1961).Theabsenceofpreservedantennaeisalsoexpectedgiven swimming, they may have used them in conjunction with the
that the antennae of modern belostomatids are small and forelegs to capture and hold prey. However, only three
concealed within grooves beneath their heads (Schuh and mesothoracic legs on two specimens have been recovered to
Slater, 1995). In addition, due to the exclusive preservation of date, indicating that the absence of these setae is not yet
thedorsalsurface,nomouthpartsarevisible. definitive. Triassonepa solensis n. gen. n. sp. does, however,
The legs of Triassonepa solensis n. gen. n. sp. provide possess a setal fringe on the metathoracic legs (Fig. 4.6, 4.8–
some interesting characters for comparison with modern 4.10), indicating that they were specialized swimmers. It is
members of the Belostomatidae. One unique character of this interestingtonotethatafewspecimens(includingtwonymphs)
speciesisthestructureofitsprothoraciclegs(Fig.4.1).Though appeartohaveadoublesetal-fringe(Fig.4.8,4.9).Itisunclear
only preserved in a single specimen, the foreleg of T. solensis atthistimewhetherthisdouble-fringeisaresultoftheposition
hasanelongatetarsusthatopposesthetibia.Incontrast,modern inwhichtheywerepreserved,orifthesespecimensareadistinct
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6 JournalofPaleontology
Figure 4. Morphological comparison of the forelegs, hemelytra, metathoracic legs, and terminalia of adult Triassonepa solensis n. gen. n. sp. and extant
belostomatid species: (1) foreleg, VMNH 94671, holotype; (2) foreleg, Belostoma flumineum Say, 1832; (3) foreleg, Benacus griseus (Say, 1832) (formerly
genusLethocerus);(4)hemelytra,VMNH53881;(5)hemelytra,DiplonychusurinatorsudanensisLinnavuori,1971;(6)setalfringeonmetathoracicleg,VMNH
50230;(7)setalfringeonmetathoracicleg,BelostomaelongatumMontandon,1908;(8)doublesetalfringeonmetathoracicleg,VMNH90281;(9)doublesetal
fringeonmetathoracicleg,VMNH90279;(10)metathoracicleg,VMNH94671,holotype;(11)femaleterminalia,VMNH90281;(12)maleterminalia,VMNH
94671,holotype;(13)terminalia,DiplonychusurinatorsudanensisLinnavuori,1971.Scalebarsare1mm.
species. Measurements of body length, abdomen width, and The hemelytra of Triassonepa solensis n. gen. n. sp. also
tarsallengthhaveshownthatthesetwospecimenshavesimilar provide good features for comparison to modern taxa. The
proportionstospecimenswithasinglefringe,andthereforemay hemelytra do not appear to cover the entire abdomen of any
bethesamespecies. specimen,butthisislikelyanartifactofpreservation(Fig.4.4).
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Criscione andGrimaldi—EarliestBelostomatidfossilsfromTriassicNorthCarolina 7
Figure5. Triassonepasolensisn.gen.n.sp.growthseries:(1)InstarI,VMNH94575a;(2)InstarII,VMNH50512;(3)InstarIII,VMNH53871;(4)InstarIV,
VMNH54155;(5)InstarV,VMNH52498.Scalebaris2mm,locatedinphoto1.
Because the apical parts of modern heteropteran hemelytra are amountofuncertaintyinsomeofthemeasurements.Atotalof
thin and membranous, it is unlikely that these regions would 51nymphsweremeasuredfromtheanteriormarginofthehead
have been preserved. In addition, the abdominal spiracles of to the apex of the abdomen, yielding five size classes (Fig. 6):
T.solensisarelocatedonitsdorsalsurface,whichistypicalof Instar I, 1.6–2.3mm (mean 2.0mm); Instar II, 2.6–3.4mm
insectsthatbreatheunderwaterviaaplastron(athinfilmofair (mean 3.0mm); Instar III, 4.0–5.2mm (mean 4.6mm); Instar
heldbeneaththewingsandusedasaphysicalgill).Inorderfor IV, 6.2–7.7mm (mean 6.9mm); Instar V, 9.5–10.3mm (mean
T.solensistouseaplastron,asisdonebymanymodernaquatic 9.9mm). Each instar was ~1.5x larger than the preceding one.
insectsincludingbelostomatids(e.g.,AbedusherbertiHildago, Modernbelostomatidsalsohavefiveinstarsandshowasimilar
1935;seeGoforthandSmith,2012), itshemelytrawouldneed growthratioof1.2–1.5witheachsuccessiveinstar(Tables2,3).
tofullycoveritsspiracles(i.e.,totheedgesoftheabdomen). These ratios correspond to Dyar’s Rule, which states that an
The8thabdominalsegmentofTriassonepasolensisn.gen. insectinstaris~1.4xthesizeofitspreviousinstar.
n.sp.containstwolateral,paddle-shapedlobesandtwomedial
processes resembling respiratory tubes (Fig. 4.11). It is
Discussion
morphologicallyquitesimilartotheeighthabdominalsegment
of female naucorids (particularly Ilyocoris exclamationis Belostomatid habitats.—Due to the presence of swimming
Scott, 1874 as illustrated by Lee, 1991). This suggests that: fringes on the hind legs of Triassonepa solensis n. gen. n. sp.,
(1) T. solensis occupies a very basal position within it is reasonable to assume that this species had similar physio-
Belostomatidae,and(2)themajorityofthepreservedspecimens logyandbehaviorstomodernbelostomatids.Understandingthe
were likely female. However, two specimens (VMNH 94671, habitats of these modern belostomatids has implications for
Fig.4.12,holotype;VMNH94672,Fig.2.4)possessterminalia determiningthenatureandchemistryofancient‘LakeSolite.’
with a slightly different structure. The 8th abdominal segments Belostomatids live in a wide variety of habitats, but are
of these specimens are more elongate and possess two apical, mostcommonlyfoundinshallowbodiesofwaterwithmarginal
articulated appendages that resemble claspers. It is therefore vegetation.KashianandBurton(2000)reportedLethocerussp.
likelythatthesetwospecimensaremales. from the wetlands of northern Lake Huron in areas dominated
Immature Triassonepa solensis n. gen. n. sp. were by sedges. Belostomatids also occur in many of India’s small
separated into instars based on total body lengths (Fig. 5). freshwater lakes. Majumder et al. (2013), for example, found
Because the head was not often preserved, there is a minor twogenera(LethocerusandDiplonychus)livinginthemarginal
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8 JournalofPaleontology
Figure 6. Lengths of Triassonepa solensis n. gen. n. sp. instars and adults: 70 specimens (51 nymphs, 19 adults) were measured. The two largest adult
specimensaremales.
Table2. Meanlengths(inmm)ofthefiveinstarsofTriassonepasolensisn.gen.n.sp.(thisstudy),Lethocerusmaximus(Cullen,1969),
L.mazzai(DeCarlo,1962),Hydrocyriuscolumbiae(Miller,1961),Belostomaflumineum(Flosi,1980),B.malkini(Cullen,1969),and
Abedusbreviceps(KefferandMcPherson,1988).
T.solensis L.maximus L.mazzai H.columbiae B.flumineum B.malkini A.breviceps
Instar1 2.0 15.0 11.0 16.0 4.6 7.75 6.4
Instar2 3.0 22.5 17.0 21.0 6.2 11.00 9.1
Instar3 4.6 32.5 26.0 28.5 9.0 15.50 11.3
Instar4 6.9 46.5 37.5 37.5 11.5 22.25 15.5
Instar5 9.9 67.5 53.0 50.5 16.5 32.50 20.0
Table3. GrowthratiosTriassonepasolensisn.gen.n.sp.(thisstudy),Lethocerusmaximus(Cullen,1969),L.mazzai(DeCarlo,1962),
Hydrocyriuscolumbiae(Miller,1961),Belostomaflumineum(Flosi,1980),B.malkini(Cullen,1969),andAbedusbreviceps(Kefferand
McPherson,1988)(thesamespeciesasinTable2),calculatedbydividinginstarlengthbylengthofthepreviousinstar.
T.solensis L.maximus L.mazzai H.columbiae B.flumineum B.malkini A.breviceps
Instar2/1 1.50 1.50 1.55 1.31 1.35 1.42 1.42
Instar3/2 1.53 1.44 1.53 1.36 1.45 1.41 1.24
Instar4/3 1.50 1.43 1.44 1.32 1.28 1.44 1.37
Instar5/4 1.43 1.45 1.41 1.35 1.43 1.46 1.29
vegetation of manmade, urban lakes in Tripura, northeastern Ciocco,2013).Thesesemi-permanentwetlandsarelocatednear
India.DiplonychusrusticusFabricius,1781wascollectedfrom a shallow, saline lake, although the wetlands themselves have
both Pocharam Lake in southeastern India (Deepa and Rao, negligiblesalinity.
2007), and Loktak Lake of northeastern India (Takhelmayum In addition to shallow lakes and wetland environments,
and Gupta, 2011). Loktak Lake is unique in its possession of belostomatidsinhabitthemarginalareasofdeeplakes,suchas
phumdis, which are floating islands composed of vegetation, Lake Victoria in Kenya (Muli and Mavuti, 2001; Orwa et al.,
organic matter, and soil, among which belostomatids live. 2015). Three species were identified there: Diplonychus sp.
Belostomatidshavealsobeencollectedfromaridwetlandssuch (formerly genus Sphaerodema), Hydrocyrius sp., and Letho-
asBañadoCarilauqueninwest-centralArgentina(Scheiblerand cerus niloticus Stål, 1885. Similarly to Loktak Lake,
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Criscione andGrimaldi—EarliestBelostomatidfossilsfromTriassicNorthCarolina 9
Diplonychussp.andHydrocyriussp.werefoundtoinhabitthe Recent research by Liutkus et al. (2010) proposed that
lake’sfloatinghyacinthmats(Orwaetal.,2015). the Cow Branch Formation was a shallow, alkaline, saline,
Belostomatids are one of the few groups of aquatic rift valley lake. They presented a number of reasons for this
insects that can tolerate agriculture-affected and polluted interpretation: (1) dominance of terrestrial and nearshore-
water bodies. Belostomatids inhabit the length of the Enfranz dwelling insects and terrestrial vascular plants, (2) exquisite
RiverinEthiopia,fromthecleanheadwaterstotheagriculture- fossil preservation, and (3) presence of dolomite and absence
dominated mouth (Mehari et al., 2014). Other nepomorphs, ofquartzandzirconiumthroughoutthedeposit.
suchasnaucoridsandnepids,wereonlyfoundintheunaffected, Based on the environmental preferences of modern
upstreamareas.Additionally,Belostomasp.hasbeencollected belostomatids, their abundance in the Cow Branch Formation
intheeutrophicKipkarenRiverofKenya(Auraetal.,2011)and would indicate a shallow, nearshore paleoenvironment. The
Diplonychussp.wasfound toinhabitthemarginsofanumber toleranceofmodernbelostomatidsforpollutedandharshwater
ofpollutedBangalorelakesinsouthernIndia(Balachandranand conditionssuggeststheymayhavealsobeentoleranttoextreme
Ramachandra, 2010). Perhaps the most extreme case is the environmentssuchassaline,alkaline,riftvalleylakes.Because
collection of Belostoma sp. from hydrogen sulfide-rich Cueva belostomatids breathe air, they would be unaffected by poor
delAzufreinTabasco,Mexico(Tobleretal.,2007). water quality. However, harsh water conditions would affect
Belostomatidsarealsoknowntoinhabittemporaryenviron- organisms possessing gill respiration (i.e., Ephemeroptera,
ments such as rain pools (Fontanarrosa et al., 2009), agricultural Plecoptera, Odonata, Trichoptera, etc.), so the lack of gilled
fields(DasandGupta,2010),ricepaddies(Hendawyetal.,2005), insect nymphs of these orders within the deposit is good
and sinkholes (Blinn and Sanderson, 1989), and are common evidence for poor water quality. The only gilled insect order
inhabitantsofephemeralplayalakesinaridenvironments(Haukos reported from the Cow Branch Formation is Diptera (Liutkus
and Smith, 1992). Belostomatids have been collected in the etal.,2010).However,thisappearstobeamisidentificationof
stagnant‘buffalo-wadingpools’ofTarangireNationalParkonthe the enigmatic, gilled, larva-like arthropod, which may actually
savanna of northern Tanzania (D.G., personal observation). beacrustacean.
Merickel and Wangberg (1981) collected Belostoma flumineum In addition to belostomatids, the insects preserved in the
along the shores of two playas near Lubbock, Texas, and Cow Branch Formation are mostly terrestrial adults from the
Richardson et al. (1972) found one juvenile belostomatid in the orders Hemiptera (Sternorrhyncha), Diptera, and Coleoptera.
Jornada Playa of New Mexico. Adult belostomatids disperse to A few other taxa have been found to date, including adult
theseephemeralenvironmentsviaflight,andasaresult,areoften membersofBlattodea,Odonata,Orthoptera,Plecoptera(Fraser
foundatbrightlightsduringthenight. and Grimaldi, 2003), Thysanoptera (Grimaldi et al., 2004),
Afewstudieshaveevenreportedbelostomatidsinhabiting Mecopterida (Grimaldi et al., 2005), Amphiesmenoptera, and
brackishwaters.Angelinetal.(2010)collectedDiplonychussp. Neuroptera.Thisuniqueassemblageofterrestrialinsectsfurther
and Belostoma sp. from an estuary in southern India with a suggests that the water was toxic to gill-possessing, aquatic
salinityofbetween4‰and8‰(ppt).Siddiqi(2008)reported larvae and other sensitive groups. Moreover, Fraser and
belostomatids in the marginal areas of India’s Lake Lonar, Grimaldi(1999)notedtheabundanceofconchostracanswithin
whichisahyperalkaline,saline,craterlakewithapHof~10.5 the insect bed. Modern members of this group are most
(Siddiqi, 2008) and a salinity of up to ~6‰ (Yannawar and commonly found in ephemeral, alkaline water bodies (Tasch,
Bhosle, 2013). However, Badve et al. (1993) report that the 1969).
marginal areas of the lake near the inflow of the freshwater Liutkusetal.(2010)discussedtheexquisitepreservationof
springs have a pH closer to 7.5. It is in these areas that the theinsectfossilsasevidenceforashallowlake.Mostinsectsare
marshesexist,anditislikelythatthebelostomatidsinhabitthese completely articulated, which is quite rare for Triassic fossils
moresuitableareas. (cf.,Riek,1974;BrauckmannandSchlüter,1993;Shcherbakov
etal.,1995;Martins-Netoetal.,2008).Thelackofdisarticula-
Environmental interpretation of ‘Lake Solite’.—Like their tion suggests limited postmortem movement. If the lake had
modern counterparts, many fossil belostomatids are reported been as deep as originally suggested, the insects would likely
from shallow, lacustrine paleoenvironments (e.g., Grimaldi havedecayed,disarticulated,orhavebeeneatenbeforesettling
and Maisey, 1990; Martínez-Delclòs et al., 1995; Prokop and tothebenthiczone.Moreover,therearenofossilfishfoundin
Nel,2000).However,thiscontrastswithbothinterpretationsof theinsectlayers,furtherevidencethattheinsectswereburiedin
the paleoenvironment of the Cow Branch Formation. Olsen veryshallowwater.
et al. (1978) first described the environment as a large, deep, The geochemistry of the deposit also supports the
chemically stratified lake. This stratification would have interpretation of a saline, alkaline lake. Liutkus et al. (2010)
produced anoxic bottom waters that prevented bioturbation reported dolomitic claystone throughout the insect bed, and
and therefore allowed for exquisite fossil preservation of inmodernlakesprimaryprecipitationofdolomiteoccursmost
delicateinsectssuchasmidgesandtinyhemipterans.Although often in waters with elevated salinity, alkalinity, and with
unusualforamodernbelostomatidhabitat,otherdeeplacustrine abundantmagnesiumandcalcium(DeDeckkerandLast,1989).
paleoenvironmentshavebeenreportedtocontainbelostomatid Furthermore,thesurroundingbasinisrichinquartz,makingits
fossils.Onesuchdeposit,thelateOligoceneEnspelFormation absence in the Cow Branch deposit significant. In addition,
of Germany (Poschmann et al., 2010), has produced ten albiteisabundantinthedeposit(Liutkusetal.,2010),whichis
belostomatid fossils, four of which are adult specimens proposed to have formed by the reaction of clay, quartz, and
(Wedmann,2000). sodium under alkaline conditions (van de Kamp and Leake,
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https://doi.org/10.1017/jpa.2017.48
10 JournalofPaleontology
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